Tablets refer to a product form obtained by compressing a powder or granules and the like into a fixed shape. Since the tablets can be easily transported and enable a fixed dose to be taken easily, the tablets are the most commonly used drug form in fields such as pharmaceuticals, quasi drugs, cosmetics, functional foods and health foods. Tablets come in various types, such as uncoated tablets, coated tablets, chewable tablets, orally disintegrating tablets or effervescent tablets, depending on the content thereof and purpose of use. The tablets in various type are used in various fields.
Coated tablets are obtained by uniformly forming a coating on the surface of uncoated tablets for the purpose of masking the taste or odor of the contents of the tablets, preventing degeneration and deterioration of the components caused by humidity and the like, and improving appearance and sensation to the tongue. Coated tablets can be roughly divided into sugar-coated tablets having a coating layer mainly containing a sugar as a coating film, and film-coated tablets having a coating layer mainly containing a water-soluble polymer or a poorly water-soluble polymer as a coating film.
The sugar-coated tablets offer the advantages of effectively masking odors, having high moisture resistance and having an attractive appearance. Conversely, the sugar-coated tables have the disadvantage of having a complex production procedure since they are coated by undergoing repeated application of liquid, spreading and drying using a large amount of a sugar coating liquid containing mainly sugar. In addition, they also have disadvantages with respect to susceptibility to cracking and chipping, having a high calorie content and imparting a high moisture content to the resulting preparation.
On the other hand, since film-coated tablets can be coated using only a small amount of coating liquid, the production procedure thereof is less complex. In addition, film-coated tablets also offer the advantages of containing fewer calories and undergoing little cracking or chipping. Conversely, film-coated tablets have disadvantages with respect to low moisture resistance and little ability to mask unpleasant odors. In this manner, sugar-coated tablets and film-coated tablets exhibit opposite properties.
Therefore, thin layer sugar-coated tablets have been developed that maintain a strong masking ability with respect to odors possessed by sugar-coated tablets while having high moisture resistance and a small coated amount. Thin layer sugar-coated tablets are normally produced by sequentially coating uncoated tablets with a protective coating layer, sub-coating layer, coloring layer and polishing layer. Each of these layers is formed by a syrup containing white sugar as a base thereof, and gelatin or powdered gum arabic as a binder. Otherwise, it is also possible to form these layers by further spraying a powder such as talc, precipitated calcium carbonate, calcium phosphate or calcium sulfate as necessary. Furthermore, it is also possible to form these layers by using a suspended composition in which the powder is suspended in the syrup. The protective coating layer that coats the uncoated tablet is formed to inhibit migration of moisture content contained in the sugar coating liquid or syrup liquid used in the sub-coating layer and coloring layer to the inside of the tablet. The sub-coating layer formed on the upper surface of the protective coating layer is formed to impart roundness to the central tablet and enhance coating strength. The coloring layer is formed to inhibit air permeability and moisture permeability by forming fine crystals of a sugar component. Finally, the tablet surface is polished by forming the polishing layer. Although the coating layer of thin layer sugar-coated tablets is thinner than that of sugar-coated tablets, since these tablets are produced by coating with numerous layers in this manner, the complexity of the production procedure has been considered to be a problem.
Development has previously been carried out on coated tablets having superior masking ability and the ability to prevent degeneration and deterioration of their contents while also being able to be produced more easily.
For example, Japanese Patent Application Laid-Open (kokai) No. 2002-179559 discloses a thin layer sugar-coated tablet which is coated with 5% by mass to 60% by mass of a sugar coating liquid containing a sugar, a vehicle and a binder, relative to the total weight of the uncoated tablet, in order to mask unpleasant odors, prevent the occurrence of whiskers, stabilize a drug that decomposes at a high moisture content and reduce the size of the tablet, and a production method thereof.
In addition, Japanese Patent Application Laid-Open (kokai) No. 2003-155232 discloses a solid preparation which contains L-cysteine and has a reduced level of unpleasant odor by incorporating L-cysteine using a dry method, and a production method thereof. Japanese Patent Application Laid-Open (kokai) No. 2004-155656 discloses a sugar-coated tablet including a coating layer, which contains a powder, a binder and less than 10% by mass of a sugar, between an uncoated tablet or film-coated tablet and a sugar coating layer, in order to enhance masking effects on odor, color, taste and the like as well as reduce size and shorten production time, and a production method thereof.
On the other hand, although erythritol is preferable for use as the base of the sugar coating layer due to its strong sweet taste and low calorie level, it is difficult to form a sugar coating layer and it is easily crystallized. An example of a method for forming a sugar coating layer using erythritol is disclosed in Japanese Patent No. 4391732 that discloses a sugar-coated tablet, obtained by forming a sugar coating layer using a sugar coating liquid that inhibits crystallization of erythritol by combining the erythritol with a polyvinyl alcohol-based resin at a prescribed ratio, and a production method thereof.
In addition, Japanese Patent Application Laid-Open (kokai) No. 2004-137224 discloses that a calorie-free sugar coating layer, which has an extremely smooth texture, exhibits favorable bonding with an uncoated tablet and has adequate strength, can be formed by using a sugar coating liquid containing erythritol, hydroxypropyl methyl cellulose and gum arabic.
In addition, as an example of a method for more easily producing a thin layer sugar-coated tablet, Japanese Patent Application Laid-Open (kokai) No. 2004-155775 discloses a sugar-coated tablet obtained by forming a sugar coating layer with a single sugar coating liquid containing polyethylene glycol, pullulan, polyvinyl pyrrolidone and/or copolyvidone. Japanese Patent Application Laid-Open (kokai) No, 2004-155775 also discloses that a sugar-coated tablet, which has adequate luster and favorable slippage even in the absence of a polishing layer, can be produced by forming a sugar coating layer equivalent to a sub-coating layer and a coloring layer with this sugar coating liquid.
In addition, Japanese Patent Application Laid-Open (kokai) No. 2009-73814 discloses a coating liquid containing erythritol; at least one of calcium lactate, xylitol, and citric acid; at least one of calcium carbonate, and talc; and pullulan for producing a sugar-coated tablet having the advantages of conventional sugar-coated tablets, such as an attractive appearance and superior odor-masking ability, and adequate strength despite having a thin coating layer, a short production time, and is suitable for incorporating components that instable in water, and a thin layer sugar-coated tablet coated with that coating liquid.
In addition, as an example of a method for improving the masking ability of film-coated tablets, Japanese Patent Application Laid-Open (kokai) No. 2008-201711 discloses a coated solid preparation obtained by providing a coating film containing a partially saponified polyvinyl alcohol-based resin on a solid preparation containing L-cysteine or salt thereof.
In addition, Japanese Patent Application Laid-Open (kokai) No. 2008-260778 discloses a film-coated tablet that reduces the odor of an uncoated tablet including a film coating layer which contains a polyvinyl alcohol-based resin and of which the weight is less than 10% by mass relative to the weight of the uncoated tablet, and a method for masking odor that utilizes this film coating layer.